NEW YORK – Thousands of striking Verizon workers will return to work starting Monday night, though their contract dispute with the telecom company isn’t over yet.

Both the company and the union say they have agreed to narrow the issues in dispute and have set up a process to negotiate a new contract. But the talks are likely to be contentious. The two sides still disagree on health care benefits, pensions and work rules.

About 45,000 employees went on strike Aug. 7 after their contract expired. They work in the company’s land-line division in nine states from Massachusetts to Virginia.

Verizon says that it needs to cut costs in the traditional land-line phone business, which is in decline as more Americans switch to mobile phones. The company has proposed freezing its pension plan and switching union workers to its non-union health plan, which has higher costs for employees.

The unions counter that the land-line business supports the growing wireless business and that Verizon, which earned about $3 billion in the first half of the year, can afford to maintain the benefits in the contract that expired Aug. 6. They also say Verizon put too many proposals on the table.

Of the 45,000 striking workers, 35,000 are covered by the Communications Workers of America, while 10,000 are covered by the International Brotherhood of Electrical Workers.

Jim Spellane, a spokesman for the IBEW, said the strike occurred because Verizon “came in with an extreme set of proposals and never really moved off of them.”

Verizon spokesman Richard Young said that many of the benefits and work rules were put in place when Verizon faced much less competition in its land-line business. “The contracts are not reflective of today’s marketplace,” he said.

Spellane said that much of the traditional phone network helps support the faster-growing wireless business. And many of the technicians who went on strike install and maintain the company’s new fiber-optic network, FiOS, which provides Internet, video and phone services.

Nearly 30 percent of U.S. homes have dropped land-line service and rely on mobile phones only, according to the National Center for Health Statistics.

Verizon added 1.3 million wireless customers in the April-June quarter, for a total of 89.7 million. That growth has been helped by the addition of Apple Inc.’s iPhone in February.

Candice Johnson, spokeswoman for the CWA, said Verizon is asking $20,000 per worker in annual concessions. The company has disputed that but hasn’t offered its own figure.

Johnson said earlier this month that the union’s best-paid Verizon workers get about $77,000 a year in New York. The company puts the figure at $91,000 and said benefits average $50,000.